Technical Field
The present disclosure relates generally to alternatives to charge based memory and more specifically to resistive switched capacitor-like structures.
Background Information
In modern microelectronic devices, the dominant memory types are dynamic random access memory (DRAM), static RAM (SRAM), and flash memory. These types of memory store data as a charge state and therefore are typically referred to as “charged based memory”. For many decades, charged based memory technology has been successfully scaled down to achieve increased density at lower bit cost. However, charged based memories is gradually approaching its physical limits, such that as device size shrinks there are increasing issues involving low operating speed, high power consumption and other scaling limitations.
Memory devices based on resistive switching, such as resistive random access memory (ReRAM), are a promising alternative to charge based memory, due in part to their potential for ultra-high density, high-speed operation, nonvolatility, and compatibility with conventional complementary metal-oxide-semiconductor (CMOS) processes. Resistive switching refers to a voltage pulse induced change in the resistance of a material from a low-resistance state (“LRS”) (i.e., an “ON” state) to a high-resistance state (“HRS”) (i.e., an “OFF” state), and vice versa. Such change in the resistance between the states may be measured as an “ON-OFF” ratio.
Resistive switching is mainly observed in capacitor-like structures. As used herein, the term “capacitor-like structure” refers to a structure comprising an insulating or semiconducting layer that exhibits reversible switching. In a capacitor-like structure, the insulating or semiconducting layer is typically sandwiched between two electrodes. An induced resistance change in the insulating or semiconducting layer is generally referred to as “electroresistance”.
The resistive switching effect is widely attributed to the formation and rupture of conducting nano-filaments (CF) in an insulating matrix due to nano-ionic and thermal effects. Typically, an initial step, referred to as “electroformation”, forms the CFs in a pristine device. This prerequisite step involves the application of a sufficient voltage to the highly insulating pristine device to form CFs.
Attempts gave been made to improve the resistive switching characteristics (e.g., the ON-OFF ratio, ability to recover to the HRS, endurance to repeated switching cycles, electroresistance in the HRS, etc.) of capacitor-like structures by tailoring chemical and physical properties, to permit the manufacture of higher performance ReRAMs. A variety of approaches have been attempted, including approaches that involve annealing, active electrodes, interface engineering and nan-crystal inducing processes. However, these approaches have met with a number of problems, and the CFs produced have had various shortcomings. As a result, ReRAM development has been slow and it has yet to supplant traditional charge based memory in the overall commercial market.
Accordingly, there is a need for a new type of capacitor-like structure that may have applications in ReRAMs.